High temperature bleaching with peracetic acid



United States Patent 3,4163% HIGH TEMPERATURE BLEAHTNG WTTH PERACETECACllD Arnold M. Soolrne, Silver Spring, and Charles A. Rader, Laurel,Md, assignors to Union Carbide Corporation, a corporation of New York NoDrawing. Filed June 30, 1965, Ser. No. 468,601 2 Claims. (Cl. 8--l15.5)

ABSTRACT 0F THE DISCLOSURE Cellulosic fabrics are bleached byimpregnating the fabric with an aqueous medium containing peracetic acidwhich is essentially free of mineral acids and hydrogen peroxide andthereafter contacting the impregnated fabric with saturated steam atabout one atmosphere for no more than 30 minutes, preferably to 10minutes.

This invention is concerned with a novel method for bleaching textilefabrics with peracetic acid. More particularly, this invention relatesto a method for bleaching cellulosic fabrics with peracetic acid atelevated temperatures.

Today almost all large-scale bleaching of textiles, particularly cotton,is done with hydrogen peroxide. Although hydrogen peroxide bleaching isgenerally superior to the previously employed chlorine bleachingprocesses, it nevertheless suffers from several disadvantages. In theconventional process the fabric is padded with an aqueous hydrogenperoxide solution and the wet fabric is stored at elevated temperatures,generally about 100 C., and c0ntacted with steam for from /2 to about 2hours. For a continuous process this requires large bleaching chutes,which occupy considerable floor space and require large amounts ofsteam. Further, to obtain optimum bleaching with hydrogen peroxide, theaqueous pad bath must be at an alkaline pH, generally about 11.5, whichis normally maintained by including sodium silicate in the pad bath. Thesilicate can adversely affect the hand of the bleached fabric, tends toaccumulate in the bleaching chutes and often complicates dyeing of thebleached fabric by silicate rub marks or rope streaks.

It has been suggested that if peracetic acid was substituted forhydrogen peroxide, sodium silicate would be unnecessary and thus theassociated problems would be eliminated. However, reported attempts toeffect bleaching with peracetic acid have indicated that long times,about one hour, are necessary for optimum bleaching, and that theresults are poorer than those obtained with hydrogen peroxide. See forexample, Rosch, Deutsche Textiltechnik, 10, 191-5 (1960).

It is an object of this invention to provide a process for bleachingtextile materials, especially cotton, with peracetic acid.

This and other objects of this invention are accomplished byimpregnating the fabric to be bleached with an aqueous medium containingperacetic acid substantially free of hydrogen peroxide and mineralacids, thereafter contacting the impregnated fabric with saturated steamat atmospheric pressure for a period of time not exceeding 30 minutesand thereafter cooling the fabric to below about 100 C. .and washing thefabric. By operating in this manner we are able to obtain a degree ofbleaching equivalent to that obtained with hydrogen peroxide for longerperiods of time without serious fabric deterioration.

The reasons for applicants improved results over those of the prior art,particularly Rosch, are not fully understood, but .are believed to be(1) the absence of mineral acids, which are present in the peraceticacid employed by Rosch, and (2) the avoidance of long times at elevatedtemperatures.

The aqueous medium employed in the process of this invention containsperacetic acid free from mineral acids and hydrogen peroxide and has apH of from about 3 to about 7. It is preferred that the bath alsocontains a wetting agent to ensure uniform contact of the bath with thefabric and a sequestering agent or a compound capable of complexing withheavy metal ions.

As has been pointed out above, the peracetic acid should be free ofmineral acids. Thus, peracetic acid prepared by the acid-catalyzedreaction of acetic anhydride and hydrogen peroxide should not beemployed because of the difliculty of removing unreacted hydrogenperoxide and the mineral acid employed as the catalyst. One suitablesource for the peracetic acid is via the oxidation of acetaldehyde asdisclosed in -U.S. Patent No. 2,804,473 to B. Phillips et al.

The amount of peracetic acid employed in the bath is not highlycritical, but should be suflicient to provide from about 0.2 to about 3weight percent of peracetic acid, based upon dry fabric. Thus, theamount of peracetic acid depends upon the quantity of aqueous mediumwith which the fabric is impregnated. For example, if the fabric ispadded to about percent wet pick-up, the peracetic acid concentrationshould be from about 0.2 to about 3 weight percent. Lower degrees of wetpick-up require higher peracetic acid concentrations and vice versa.Preferred concentrations at 100 percent wet pick-up are in the range offrom about 1 to about 2.5 weight percent.

The bath should be at a pH of from about 3 to about 7, with a pH of fromabout 4.5 to about 6.5 being preferred and a pH of about 5.5 beingoptimum. The desired pH is obtained in any desirable manner, preferablyby the addition of suitable amounts of an alkali metal hydroxide, forexample, sodium hydroxide or potassium hydroxide. The aqueous peraceticacid solution normally has a pH of 3. To obtain a pH of about 5.5,sodium hydroxide is added in a weight ratio to peracetic acid of about0.2: 1.

Wetting agents which can be employed in the process of this inventionare known to the art, and include alkali metal sulfates of long chainalcohols, alkali metal sulfonates of ethylene oxide adducts of acohols,alkali metal sulfonates of alkylphenols and the like. While notessential to this invention, they are desirably employed in amounts offrom about 0.1 to about 1 weight percent.

sequestering agents, although not essential, are desiraby present in thebath in amounts of from about 0.05 to about 1 weight percent. Suitablesequestering agents are known to the art, and include alkali metalsalts, preferably sodium salts, of condensed phosphates, such as sodiumhexametaphosphate, sodium pyrophosphate, sodium tripolyphosphate and thelike.

After impregnation with the aqueous medium, the fabric is contacted withsaturated steam at atmosheric pressure, i.e., at about 100 C. for aperiod of not more than 30 minutes. Times in excess of 30 minutes cannotbe employed because of the serious fabric deterioration resulting fromsuch extended times. Times of from about 5 to about 10 minutes arepreferred.

The bleached fabric is then cooled to below about 100 C., Washed toterminate the bleaching action of the peracetic acid, and then dried.

The following example is illustrative. In the example, the bleachedfabrics were evaluated by the following techniques.

(1) Refleczance.Determined with a Hunter Multipurpose Reflectometeremploying green, blue and amber filters, with the reflectometercalibrated to read 100% reflectance from a magnesium oxide block. Greenand blue reflectances are reported as percents of the reflectance 3 froma magnesium oxide block. Whiteness was calculated by the equation:

Whiteness: (4 blue reflectance) (3 X green reflectance) Yellowness indexwas calculated by the equation:

amber reflectanceblue reflectance green reflectance (2)Fluidity.A.A.T.C.C. Standard Test Method 82- 1961 as modified by H. C.Lindley, Rapid Dispersion of Cellulose in Cuene, Textile Res. 1., pp.2867, February 1951.

Ycllowness= Example 1 A piece of 80-inch by 80-inch scoured cottonprintcloth was padded to about 100 percent wet pick-up with an aqueoussolution having a pH of 5.5 and containing 2.37 weight percent peraceticacid, 0.5 weight percent sodium lauryl sulfate as a wetting agent, 0.2weight percent sodium hexametaphosphate as a stabilizer and 1.25

as Run 1.

TABLE I Run No.

Control Time, min 5 10 20 Blue reflectance. 37v 8 88. 6 90. 2 90. 0 (i5.2 Green reflectance 90. 6 91. 0 92. 2 92. 6 72. 1 whiteness 70. 2 81. ti80. 2 84. 8 44. Yellowncss index 0. 04 0. 03 0. 03 0. 0L. 0. l2Fluidity, rhes 1. 05 3. 27 0. 70

As is readily seen, the process of this invention provides a high degreeof bleaching in from 5 to 10 minutes (Runs 1 and 2) with some additionalimprovement being obtained at a time of about 20 minutes (Run 3). Littlefurther bleaching occurs on heating for longer times, such as one hour(Run 4), and the main effect of this additional heating is to promoteoxidative degradation of the cotton, as is indicated by the approximatedoubling in fluidity in going from 20 minutes to minutes.

What is claimed is:

1. In the method for bleaching a cellulosic fabric which comprisesimpregnating the fabric with an aqueous medium containing peracetic acidand thereafter heating said impregnated fabric at elevated temperatures,the improvement of (1) employing an aqueous medium essentially free ofmineral acids and hydrogen peroxide, and (2) contacting the impregnatedfabric with saturated steam at about atmospheric pressure for a periodnot in excess of 30 minutes and thereafter washing said fabric.

2. In the method for bleaching a cellulosic fabric which comprisesimpregnating the fabric with an aqueous medium containing peracetic acidand thereafter heating said impregnated fabric at elevated temperatures,the improvement of (1) employing an aqueous medium essentially free ofmineral acids and hydrogen peroxide, and (2) contacting the impregnatedfabric with saturated steam at about atmospheric pressure for a periodof from about 5 to about 10 minutes and thereafter washing said fabric.

References Cited UNITED STATES PATENTS 2,347,434 4/1944 Richert et al.8111.5 XR 2,442,332 6/1948 Haney et a1 8111.5 XR 2,590,856 4/1952Greenspan et al. 8111.5 XR 2,804,473 8/1957 Phillips 260-502 FOREIGNPATENTS 901,687 7/1962 Great Britain.

OTHER REFERENCES Roesch, Darstellung und annending von Peressivesaure inder Bleicherei. Deutsche Textiletchnik 10 (1960), pp. 191-195. Use ofPeracetic Acid for Bleaching Nylon Textiles, The Textile Manufacture,January 1955, pp. 4243.

NORMAN G. TORCHIN, Primary Examiner.

I. P. BRAMMER, Assistant Examiner.

U.S. Cl. X.R. 8-1 15

